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The safe lander dynamics is an important part of the lunar landing mission. In this paper, a discrete element method (DEM) for lunar soil is set up, and the finite element method (FEM) for the lander is set up by shell elements and beam elements. The lander is regarded as a multibody system composed of a cabin, legs and footpads, and its motion characteristics are solved by multibody dynamics (MBD). A DEM-FEM-MBD coupling algorithm is developed to simulate the landing process of the lander considering landing mode and buffer mechanism, whose correctness is verified by comparison with a full-scale experiment involving lunar lander on earth. The effects of the mass, landing velocity and attitude of the lander on the safe landing are discussed. The buffering mechanism and influencing factors of lunar soil are analyzed. The results show that the impact force peak and impact depth gradually increase with the increase in the landing velocity and mass of the lander. Two kinds of inclined landing modes are defined and compared with vertical landing. It is found that the force on the landing leg that first contacts the lunar soil is significantly greater than that on the landing leg, that contacts later. The impact force peak on the lander under the two inclined landing modes is similar, but the impact depth of the 1-2-1 mode is significantly greater than that of the 2-2 mode. In the process of landing, lunar soil has the function of buffering dissipation. The energy dissipation rate is affected by the physical characteristics of lunar soil and the mechanical energy of the lander.

The coordination of time steps directly affects the accuracy and efficiency of the calculation results in the simulation of the interaction between particles and structures. In this paper, a coordinated time-stepping method for coupling is proposed. The discrete element method (DEM) is used to establish the particle model, and the finite element method (FEM) and multibody dynamics (FEM-MBD) are applied to establish the structural model. The time step of the coupling algorithm between particles and a structure is discussed. The calculation efficiency and accuracy of the above methods are verified by an impact model, particle free falling model and electric pendulum model. Finally, the factors affecting the calculation efficiency of the coupling algorithm are discussed. The results show the following: compared with the theoretical solution, the calculation results of the coordinated time-stepping method are accurate. The multiple relationships of time steps between DEM and FEM-MBD are defined as communication coefficients, and the selection of a communication coefficient of 10 or 50 can effectively improve the calculation efficiency. When the communication coefficient continues to increase, the improvement of the calculation efficiency is not obvious. The number of structural elements has a great impact on the calculation efficiency, the number of particles in a certain range has a small impact on the calculation efficiency, and the time step of the DEM has a great influence on the calculation efficiency. The coordination time step method can improve the efficiency of the calculation while ensuring the accuracy of the calculation.

This paper discusses the safe landing process of a reentry capsule in detail with respect to landing attitude and rebound response. First, the discrete-element method (DEM) of the land soil...

The plant water consumption and irrigation management are the core issue of the sustainable growing of the Tarim Desert Highway shelterbelt in the hyperaride Taklimakan Desert. The stem sap flow, water status and water consumption of shelterbelt plants were studied, then, the issue of the water save in the process of shelterbelt irrigation management was discussed by measuring the sap flow of shelterbelt plants with a stem sap flow gauge. The stem sap flow exhibited a distinct diurnal course with maximum values between 10:00 and 15:00, and minimum values between 00:00 and 03:00. Generally, sap flow was lower at night than during the day. The daily average stem sap flow of Calligonum arborescens, Tamarix ramosissima and Haloxylon ammodendron (diameter 1.9–2.0 cm) was 67.2 g·h−1, 77.05 g·h−1 and 61.54 g·h−1 respectively. The sap flow was influenced by environmental factors, and the solar radiation, wind velocity, temperature and relative humidity were significantly correlative with plant stem sap flow. The annual water consumption of 8-a Calligonum arborescens, Tamarix ramosissima and Haloxylon ammodendron was 1937.80 kg, 1253.39 kg and 1026.96 kg, while daily average water consumption was 9.69 kg, 6.27 kg and 5.13 kg respectively. Under drip irrigation, soil moisture content of the shelterbelt in different months indicated no obvious fluctuation, and soil moisture was adequate. The predawn and midday plant water potential reflected that the plant water status was in good conditions. There is still some water-saving space if optimizing the present water management, integrating water resources conservation and protection performance.

Under the native habitat conditions, the seasonal gas exchange characteristics of two natural endemic plant species, Calligonum taklimakanensis B.R. Pan & G.M. Shen and Tamarix taklamakanensis M.T. Liu, which are located in the hinterland of the Taklimakan Desert, are measured and compared by Li-6400 photosynthesis system. The results indicate that temperature (°C), solar radiation (PAR), soil water content (SWC), and other environmental factors have obvious seasonal variations and the gas exchange characteristics of two plants have different changes in different growing seasons. For C. taklimakanensis, both in July and September, its daily changes of net photosynthetic rate tend to be obvious double peak curve, but in July its peak appeared earlier. Besides its maximum net photosynthetic rate (Pmax), apparent quantum efficiency (Φ), range of effective photosynthetic radiation significantly less than that in September. Moreover, its water use efficiency (WUE) in July was also lower than that in September due to the higher transpiration rate (Tr). For T. taklamakanensis, although its daily change of net photosynthetic rate is a single peak curve in September, its peak time has not changed, and except that its WUE is higher in September like C. taklimakanensis, the maximum net photosynthetic rate (Pmax), apparent quantum efficiency (Φ), light saturation point, and range of effective photosynthetic radiation has not changed or slightly declined. That is to say C. taklimakanensis select a season that habitat was better (like September) to progress relative effectively photosynthesis accumulation, in contrast, T. taklamakanensis still keep a relatively stable photosynthesis rate in different growth seasons. The difference of gas exchange characteristics of the two plants in different seasons shows that adaptation strategies of the two plants to extreme conditions in desert are different. Besides, both the higher photosynthetic accumulation rate and the higher water use efficiency in September also indicate that these two endemic desert shrubs possess the abilities and strategies to make the best of limited natural resources.

Calligonum. taklimakanensis B.R.Pan et G.M.Shen is an indigenous species that grows in the Taklimakan Desert. This study shows the relationship between C. taklimakanensis B.R.Pan et G.M.Shen and water conditions in the hinterland of the desert. The results show that: (1) Depth of water table is an important factor that affects water potential (Psi(p), Psi(A)), osmotic potential (Psi(sat), Psi(tlp)), relative water content (RWCtlp, ROWCtlp), and transpiration rate. (2) The degree of mineralization has a significant impact on the water potential of plants. A high degree of mineralization can strongly reduce plant productivity. (3) C. taklimakanensis B.R.Pan et G.M.Shen reduces the temperature of assimilation sticks through a high transpiration rate and maintains relatively high water content to adapt to drought and hot weather conditions in the hinterland of the desert. In addition, C. taklimakanensis B.R.Pan et G.M.Shen adapts to the water status in the desert through self-regulation or even sacrificing productivity.